Co-ops and internships are all the same. It's just how the work term is divided up that's different. With co-ops, you start your co-op in your 3rd year (of a degree that's normally 4 years). You go to uni the first 4 months (one semester), then you go back to school for another 4 months, and then continue alternating until your degree is finished. You end up with 16 months total work.
Sometimes, they'll make you go to uni for 8 months, then you get an 8 month co-op, go back to uni for 8 months, have another 8 month work co-op, and you finish off your degree by going back to uni for your last 4 or 8 months. It really depends.
Internships either have 8 month work terms similar to what I just described, or they just work for 16 months straight and never have to go back to uni during that time.